Fluidized bed reactors usually comprise a reaction chamber for combusting or gasifying fuel and at least one discharge channel connected to an upper portion of the reaction chamber for discharging exhaust gas and solid particles from the reaction chamber to a particle separator. Solid particles are separated from the exhaust gas in the particle separator so as to return at least a portion of the particles via a return channel to a lower portion of the reaction chamber.
Particle separators used in fluidized bed reactors, especially in fluidized bed boilers, are generally cyclone separators having a cylindrical upper portion and a conical lower portion. According to a conventional construction, the cylindrical upper portion has a circular cross section, but during the last two decades, polygonal cross sections, such as square or octagonal cross sections, have become more and more common. Correspondingly, the cross section of the conical lower portion can vary from circular to different polygonal shapes.
According to current design practice, the walls of the reaction chamber, as well as those of the particle separator, are water-tube panel walls that consist of vertical water tubes and plate-like fins between the tubes. A problem of such water tube walls is that the strength of the walls can be, in view of their size, relatively weak, so that they cannot bear heavy stresses or pressure differences generated by the combustion of fuel in the reaction chamber. Therefore, water tube walls are generally reinforced by a support construction, usually, by so-called buckstays attached to each side wall of a reaction chamber. Such beam-like buckstays are generally firmly attached to a central portion of each side wall, but the connections to edge portions of the side walls enable axial relative movement of the beam so as to allow differential thermal expansion of the beam and the wall. Compensation of loads generated by pressure differences over a wall are thereby assisted by bending stress of the corresponding beam.
British patent document number GB 1,009,034 discloses a cooled supporting framework for the tube walls of a rectangular combustion chamber or gas pass of a steam boiler. The supporting framework comprises continuous or sectioned ring frames arranged horizontally around the combustion chamber or gas pass. The ring frames may be constructed from hollow tubes of circular or rectangular cross section so as to circulate cooling fluid through the tubes. Such cooled ring frames are difficult to construct and tend to be too weak to prevent bending of the walls. British patent document number GB 1,015,838 shows an improvement of the design of British patent document number GB 1,009,034, in which cooled ring frames are further supported by conventional steel support beams.
The walls of a particle separator having a polygonal cross section can be reinforced by connecting horizontal beams to each of the walls, so as to form a frame corresponding to an outer circumference of the particle separator. A large particle separator is supported by a plurality of such frames attached at different levels to the walls of the particle separator. However, this may require a lot of construction phases, such as welding or bolting, which adds to the construction costs and makes the separator structure heavy in weight.
U.S. Patent Application Publication No. 2010/0024694 and European patent document number EP 0 763 384 disclose particle separators connectable to a fluidized bed reactor, which separators comprise a vertical vortex chamber with a polygonal cross section formed by a plurality of tube panel walls. U.S. Pat. No. 6,802,890 discloses an assembly of octagonal particle separators attached to a reaction chamber of a fluidized bed reactor. Parallel walls of the particle separators, and also, parallel walls of the separators and the reaction chamber, are supported against each other by using horizontal support beams. This construction requires heavy support beams and, still, it does not provide support to each of the panel walls of the octagonal particle separators.
An object of the invention is to provide a particle separator assembly of a fluidized bed reactor, in which the weight is reduced, and the performance is improved, as compared to the prior art solutions.